1. Technical Field
The present invention relates to an atomic cell, a manufacturing method for the atomic cell, a quantum interference device, an atomic oscillator, an electronic apparatus, and a moving object.
2. Related Art
As an oscillator having a highly accurate oscillation characteristic for a long period, there is known an atomic oscillator that oscillates on the basis of energy transition of atoms of alkali metal such as rubidium or cesium.
In general, operation principles of atomic oscillators are roughly classified into a system that makes use of a double resonance phenomenon by light and a microwave and a system that makes use of a quantum interference effect (CPT: Coherent Population Trapping) by two kinds of light having different wavelengths. Both the atomic oscillators include a gas cell (an atomic cell) in which alkali metal is encapsulated (see, for example, United States Patent Application Publication No. 2005/0184815 (Patent Literature 1)).
As such an atomic cell, as disclosed in Patent Literature 1, there is known an atomic cell in which a hole piercing through the atomic cell is sealed by glass. In the atomic cell disclosed in Patent Literature 1, coating for preventing reaction or diffusion of the alkali metal to the glass forming an inner wall surface is applied to the inner wall surface.
However, in the atomic cell disclosed in Patent Literature 1, coating is not applied to an inner side opening of the hole for sealing. Therefore, the behavior of the alkali metal becomes unstable. As a result, there is a problem in that frequency stability is deteriorated. The hole for sealing is used, for example, when the alkali metal is introduced into an internal space. Therefore, a certain degree of size has to be secured for the hole for sealing. On the other hand, in recent years, there is a demand for a small atomic cell according to a demand for a reduction in the size of an atomic oscillator. A ratio of the area of an opening of the hole for sealing to the area of the inner wall surface of the atomic cell increases. Therefore, such a problem becomes conspicuous.